National surveys show that nearly 50% of American women are dieting at any one time. While large numbers of people are losing weight, gaining weight, and weight cycling, relatively little is known about the positive and negative consequences of these patterns. What evidence exists suggests negative effects on behavior, metabolism, and health. We propose that repeated episodes of weight loss and gain lead to: 1) detrimental changes in eating behavior and dietary patterns (behavioral variables); 2) adverse effects on glucose tolerance, blood pressure, adiposity, regional fat distribution, and energy balance. These changes may be manifest in healthy young women prior to pregnancy or it may take a biological challenge such as pregnancy to make them evident. Pregnancy makes unique demands on metabolism and insulin economy and on energy storage and utilization. Because of the changes hypothesized to be caused by weight cycling history, there may also be increased risk for the development of gestational diabetes or hypertension as well. A prospective study of women prior to and during pregnancy will test these hypotheses. Participants will be selected on the basis of their weight (overweight vs. average weight) and their history of repeated episodes of gaining and losing weight.